Fluorescent tracers have been employed to detect leaks in fluid systems such as refrigeration systems, which utilize hydrocarbon refrigerants and lubricants. The site of a leak the refrigerants and refrigerant lubricants which contain the fluorescent tracer escape; they are visible when illuminated with light having wavelengths in the range of 300 to 450 nanometers.
The refrigerant are typically hydrofluorocarbons, hydrochlorofluorocarbons, and mixtures thereof. Common refrigeration lubricants are polyalkylene glycols, polyolesters, mineral oil, polyalphaolefins, and synthetic hydrocarbons.
Traditionally, the typical fluorescent dyes that have been used in fluroescent tracers for refrigeration systems are rhodamine B, Fluorescent Yellow 133SC, auramine B and certain conventional naphthalimide dyes. Some of these dyes are unstable at high temperatures and may be converted to tars, which plug the system. Other dyes have low solubility in the refrigerants and refrigerant lubricants which results in aggregates of precipitated dye circulating through the system. Some of these dyes, while showing good initial solubility in the refrigerants and refrigerant lubricants, tend to be unstable over storage and operation time thus resulting in aggregates of precipitated dye circulating through the system. These aggregates may clog the refrigeration system.
Conventional naphthalimide dyes are fluorescent in polyalkylene glycols, and other polar lubricants. However, naphthalimide dyes have limited solubility in the polar lubricants, and very low solubility in non-polar lubricants such as mineral oil, synthetic oil, and motor oil. The fluorescence of the naphthalimide dyes is often severely limited by the poor solubility. Furthermore, the naphthalimide dyes require long mixing times and/or elevated temperatures to dissolve the dye into the lubricant. Dissolution at elevated temperatures results in solutions that are supersaturated at room temperature. These supersaturated solutions tend to precipitate dye either in the lubricant during shelf storage, or in the refrigerant system during long term operation. The presence of precipitated dye tends to decrease the fluorescence of the solution, thus reducing its effectiveness, and also tends to clog the refrigerant system.
A fluorescent dye that is soluble in refrigerants and refrigerant lubricants, chemically stable at high temperatures and provides improved shelf stability is desirable.